Bows have been used for a very long time and many improvements have been made during the years. The most recent type of bow is the compound bow. The compound bow uses pulleys or cams in order to maximize the energy that is stored in the tensioned bow. A compound bow comprises two idler wheels, one located on the top portion and one on the bottom portion of the bow, which reels out the bowstring in a non-linear relationship against limb bending or pull. To enable this functionality, there is a need for “span ratio” which can be different between compound bow designs.
The wheels work together in a force balance configuration. Each of these wheels have cams to variate bowstring reel out versus limb pull. To enlarge the span that can be directly achieved from the cam system, high force cables connect between the upper and lower idler wheel arrangements. A problem with such compound bows is that the idler wheels are moving mainly vertically when the bowstring is tensioned and released, making it more or less impossible to synchronize the rotation of the upper and lower idler wheels respectively. A synchronized rotation of both wheels is desirable since it reduces the hit dispersion.
A well-known problem in the art is nock travel, which directly influences hit dispersion. When the idler wheel is carried on the limb tops, a number of error sources makes the bowstring groove in the idler wheel to move sideways resulting in horizontal nock travel. One example of such error source is from limbs not having equal characteristics over the full draw, making the idler wheel to twist. This means that the nocking point of the bowstring is not mowing in a straight line after release.
Another error source is unsymmetrical loading to risers and limb systems making the system bend or twist. Sideways unsymmetrical risers are commonly used in opposite to shoot through solutions that can be symmetrical. The unsymmetrical riser has a central part at the arrow rest, which is located to the side of the bowstring to enable free passage of the arrow fins, resulting in a sideways bending of the whole system. The arrow nocking point will not move in a straight line after release.
In a conventional compound bow, idler wheel rotation depends on a force balance between upper and lower limbs resulting in a vertical nock travel as the two idler wheels are not rotating synchronously. Since the idler wheels are moving, it is more or less impossible to eliminate this error source by a synchronizing system.
Another problem with prior art compound bows is that it has a draw stop, which acts against the high force interconnecting limb cable, i.e. the draw stop is a soft stop. For an unskilled shooter, this will result in considerable draw length variations that results in errors from variations in arrow speed and making the bow string peep sight move up and down. Variations in the shooter's draw length will result in dispersion primarily at long shooting distances.
Prior art compound bows are disclosed in U.S. Pat. No. 6,776,148B1, U.S. Pat. No. 3,851,638A, US451236A, U.S. Pat. No. 8,387,604B1 and disclose bows with idler wheels which are movably arranged, and thereby contributing to a large hit dispersion. From the above it is understood that there is room for improvements.